Kino Der Untoten, which is available right at the start of the game. The Pentagon, which is available after you have completed the story mode. Dead OPs Arcade.

To unlock this game mode you are going to need to do the following, 1. Go to the main screen where it says Campaign, Multiplayer, Zombies and Options. 2. Press the LT and RT buttons simultaneously for 4 seconds then press B your character is free from the chair (You get an achievement as well) 3. Walk over to the computer and press X (You unlock a gamer Picture) to use it. A CMD type screen will appear. 4. Type "DOA" and press enter. 5. Enjoy!

Note- You will not need to do this every time you want to play this game, just go to Zombies and it will be listed there.